As a solid state image sensing device, a CCD type solid state image sensing device and an MOS type solid state image sensing device are known. The MOS type solid state image sensing device can be driven by a single power supply, and an image pick-up section and a peripheral circuit can be manufactured in an MOS process to be constituted as one integrated circuit. In recent years, the MOS type solid state image sensing device attracts attention from these advantages. Moreover, the MOS type solid state image sensing device amplifies with a transistor a signal detected in a photoelectric-conversion section, and has a feature of being high sensitivity. Moreover, the MOS type solid state image sensing device is expected to be suitable for reduction of the pixel size by the increase in the number of pixels, or reduction of an image size.
With reference to FIGS. 10 and 11, description will be given of the conventional solid state image sensing device. A cross-sectional structure of a unit cell of the conventional solid state image sensing device is shown in FIG. 10. FIG. 10 is a cross-sectional view of a region including a photodiode and a read-out transistor in the unit cell of the conventional solid state image sensing device. This conventional semiconductor device is described in Japanese Patent Publication (Kokai) No. PS61-26270.
A P-type well 202 is provided in an upper part of a P-type silicon substrate 201, and an isolation region 203 is provided in the P-type well 202. An N-type signal accumulation region 204 is provided in an upper part of the P-type well 202 with a space from an upper surface of the P-type well 202. Moreover, in the upper part of the P-type well 202, a P-type shield region 205 is provided between the upper surface of the P-type well 202 and the signal accumulation region 204. The photodiode of the unit cell includes the P-type well 202, the P-type barrier region 205 and the signal accumulation region 204. Moreover, alight filter (not shown) is provided over the P-type well 202, and faces the signal accumulation region 204. A spectral characteristic of the photodiode is dependant on a spectral characteristic of the light filter.
An N-type drain region 206 is provided in the upper part of the P-type well 202 with a space from the signal accumulation region 204. On the P-type well 202 between the signal accumulation region 204 and the N-type drain region 206, a gate electrode 208 is provided with a gate insulator layer 207 (not shown) interposed therebetween.
The signal accumulation regions and peripheral regions of three adjacent photodiodes in the conventional solid state image sensing device are shown in FIG. 11. First signal accumulation region 204a, second signal accumulation region 204b and third signal accumulation region 204c are provided in the upper part of the P-type well 202 with a space from each other. Moreover, first P-type shield region 205a, second P-type shield region 205b and third P-type shield region 205c are provided on the signal accumulation regions 204a, 204b and 204c in the upper part of the P-type well 202. The signal accumulation regions 204a, 204b and 204c are photodiodes, each of which has a different spectral characteristic with each other.
In a case where a color arrangement of a pixel by a photodiode is RGB color arrangement (Red, Green, Blue), first signal accumulation region 204a is a photodiode for red light, second signal accumulation region 204b is a photodiode for green light and third signal accumulation region 204c is a photodiode for blue light. An optical charge density generated by an incident light with longer wavelength (red>green>blue) is distributed over a deep position of the P-type well 202 because of an electrical property of the silicon substrate which is the P-type well 202.
In recent years, a distance between adjacent photodiodes is becoming short with reduction of pixel size. Therefore, in the above-mentioned conventional solid state image sensing device, it is possible that signal charge generated in a deep position of silicon substrate by an incident light with long wavelength (red) enter into a signal accumulation region of an adjacent photodiode as shown in the arrow of FIG. 11. Thus, when signal charge enter into the adjacent photodiode for green light and the adjacent photodiode for blue light from the photodiode for red light with long wavelength, an increase of a color mixture and a dark current has been seen as a problem.